Insulating bushing with pressurelimiting means



June 17, 1952 J. DORMONT 2,600,979

INSULATING BUSHING WITH PRESSURE-LIMITING MEANS Filed April 15, 1948 h 2 SHEETS--SHEET 1 Fig l.

FRANG/BLE Inventor: Jean Dor'mont, by Hls Attorney.

June 17, 1952 DQRMONT 2,600,979

INSULATING BUSHING WITH PRESSURE-LIMITING MEANS Filed April 13, 1948 2 SHEETS SHEET 2 Fig. 1. 15

KEV"

' Invent or:

Jean Dor'montl,

His Attorney Patented June 17, 1952 UNITED STATES PATENT OFFICE INSULATING BUSHING WITH PRESSURE- LIMITING MEANS ration of New York Application April 13, 1948, Serial No. 20,712 In France July 28, 1947 1 Claim.

This invention relates to insulating bushings and more particularly to insulating bushings for use with transformers or other similar electrical apparatus.

Insulating bushings are used when it is necessary to pass the connecting leads of electric apparatus through the cover or walls of such apparatus. In the case of high voltages and electric apparatus which are immersed in a dielectric liquid such as oil the insulating bushing consists normally of two insulators generally made of a ceramic material such as porcelain. They are assembled by means of a metal fitting which is fastened to the wall or cover of the tank in which such electric apparatus is contained. The outer insulator is usually equipped with fins or corrugations the inner insulator, which is immersed within the dielectric liquid may be smooth. The insulation, in a radial sense, is obtained by an assembly of insulating cylinders that are mounted concentrically with respect to the central conductor through which the connection to the outside is realized. A series of metal elements embedded within the cylinders permit an appropriate electric field distribution. The assembly is filled with a dielectric liquid; a gage on top of the bushing serves to indicate the level of the dielectric fluid, and a normally spherical container allows for the expansion of the liquid.

This well-known arrangement has certain shortcomings. The dielectric liquid which is enclosed within the insulating bushing may deteriorate, in time, due to the efiects of the electric field, oxidation and the variation of temperature. Also there is a tendency for moisture to pass through the bushing and thus contaminate the dielectric fluid.

To overcome these shortcomings, rather than have the bushing a completely self-contained unit, the lower insulating element of the bushing is often eliminated and the dielectric fluid in which the electric apparatus, such as a transformer, is immersed is allowed to pass within the bushing. In this case the conservator, which assures that the electric apparatus is completely filled with dielectric fluid and that no air is Dresent, is mounted above the highest point of the bushing, thus making certain that the bushing also is completely filled with liquid. Since there is no air present oxidation of the dielectric liquid is prevented and, due to the liquid in the conservator, the bushing is under a slight outward pressure preventing the entrance of moisture. Also, since the dielectric fluid is no longer confined within the bushing it may circulate and renew itself. However, this arrangement has one disadvantage; when an accident in the immersed electric apparatus causes an appreciable pressure rise withinthe tank this pressure rise is transmitted immediately to the outer insulating element of the bushing, and since this outer element is usually made of some frangible material the bushing may crack before a safety valve or automatic pressure relief device has had time to operate.

In accordance with this invention a muffle or battle arrangement is provided between the inner wall of the insulator shell and the interior of the tank. These baffles permit the normal circulation of the dielectric liquid but delay the propagation of abrupt internal pressure rises within the frangible bushing, thus affording time for the safety valve to operate and avoid breakage of the insulator.

It is an object of the invention to provide a new and simple insulating bushing for electric apparatus which is filled with a dielectric fluid.

Another object of this invention is to provide an insulating bushing which is open to its attached electric apparatus and allows for the interchange of dielectric liquid.

A further object of this invention is to provide such a bushing constructed normally of a frangible ceramic material which will not rupture due to a sudden appreciable pressure increase in the dielectric fluid within the tank containing the electric apparatus on which the bushing is mounted.

This invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claim.

In the drawing Fig. 1 is an elevation of a high voltage transformer and its accessories which incorporates a particular embodiment of this invention. Fig. 2 is an elevation, partly in section, of a high voltage bushing made in accordance with this invention. Fig. 3 is a bottom view of the high voltage bushing shown in Fig. 2.

Referring now to the drawing there is shown in Fig. l, by way of example, a high voltage transformer I having a tank 2 which is filled with any suitable dielectric and cooling liquid such as oil 3. The tank 2 is provided with fins or radiators for the purpose of cooling the transformer oil 3. Mounted on the tank cover 5 of the transformer tank 2 is an entrance bushing 6, prepared in accordance with this invention, through which passes a high voltage conductor 1' from transformer unit '7. An oil conservator 8 which is connected to the transformer tank 2 by means of a pipe 9 is mounted so that it assures that both the transformer tank 2 and the bushing 6 are completely filled with the dielectric fluid 3. Also mounted on the tank cover 5 is a safety pipe 10 which is closed at the upper end by a frangible diaphragm H. The diaphragm I! is of such a thickness that it will fracture as soon as the pressure within the safety pipe 10 reaches some specific previously determined value.

The entrance bushing 6 is illustrated in greater detail in Fig. 2 and consists of an external insulator (2 made of porcelain, or some other similar ceramic material, within which are mounted, concentrically with respect to the central conductor 1, a certain number of insulating cylinders IS in which may be embedded metallic elements M for bringing about a favorable distribution of the electric field. Cylinders l3 are separated from one another b means of insulated spacing elements I5 which are positioned between the upper and lower ends of the cylinders 13. The insulating spacing elements I5 are ring-shaped and constitute confining walls that close the annular space between the cylinv ders l3, and, consequently, impede the flow of oil 3 between the tank 2 and the inner wall of the insulator l2. Therefore, small holes or orifices 16 are drilled in the spacer rings 15 to allow for restricted flow of the dielectric liquid 3.

It is preferable that the holes I6 in the upper and lower spacer rings 15 do not have the same vertical axis in common, as has been shown in Fig. 2, but rather the holes 16 should be staggered.

The tube assembly 13 is held together by the metal fitting I! which also has been drilled so as to provide it with small holes l8. The fitting I1 is secured to the base [9 of the bushing '6 by means of screws 20. The porcelain insulator I2 is fastened to the annular base 19 by means of the joint 2|, the collar 22, and the screws 23. A collar 24 is fastened to the upper extremity of the porcelain insulator l2, and has fastened to it the terminal fitting 25. An orifice which is normally closed by means of a screw 26 acts as a vent and is opened when the transformer l is being filled with the dielectric liquid 3. The complete bushing 6 is tightly fastened to the transformer tank cover 5 by means of gasket 21 and screws 28.

Therefore, in case of an accident and an abrupt substantial increase in pressure within the tank 2 of the transformer I the pressure wave will not be transmitted immediately to the porcelain insulator l2; for prior to the surge reaching the While there has been shown and described a particular embodiment of this invention it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

Electrical apparatus comprising a container, an electrical unit mounted in said container, said electrical unit including a conducting lead extending therefrom to the exterior of said container, a hollow porcelain insulating member mounted externally of said container and supporting said conducting lead, a plurality of concentric tube members mounted Within said hollow insulating member and extending therefrom to the interior of said container, a mounting flange for said tube members, a plurality of orifices in said flange in communication with the interior of the hollow insulating member and container. said tube members having annular spacers mounted at the extremities thereof, said annular spacers having orifices therein, means including a conservator mounted above said container for causing a dielectric fluid to flll said container and said hollow insulating member, the circulation of said dielectric fluid being restricted by said annular spacers and said dielectric fluid flowing solely through said orifices, and pressure relief means mounted on said container, said orifices being of such restricted size as to protect said porcelain insulating member from a sudden pressure rise in the fluid in said container until said pressure relief means has time to operate and relieve said pressure rise.

JEAN DORMONT.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 1,688,737 Moody Oct. 23, 1923 1,726,095 Austin Aug. 27, 1929 1,774,946 Rankin Sept. 2, 1930 1,786,729 Austin Dec. 30, 1930 1,983,370 Hillebrand Dec. 4, 1934 1,996,423 Jansson Apr. 2, 1935 2,188,417 Rorden Jan. 30, 1940 2,263,768 Frakes Nov. 25, 1941 2,381,787 Terpak et al Aug. 7, 1945 FOREIGN PATENTS Number Country Date 294,938 England Jan. 17, 1929 

